Room temperature purification of few-walled carbon nanotubes with high yield

A Review of the Use of Carbon Nanotubes and Graphene-Based Sensors for the Detection of Aflatoxin M1 Compounds in Milk

This paper presents a comprehensive review of the detection of aflatoxin compounds using carbon allotrope-based sensors. Although aflatoxin M1 and its derivative aflatoxin B1 compounds have been primarily found in milk and other food products, their presence above a threshold concentration causes disastrous health-related anomalies in human beings, such as growth impairment, underweight and even carcinogenic and immunosuppressive effects. Among the many sensors developed to detect the presence of these compounds, the employment of certain carbon allotropes, such as carbon nanotubes (CNTs) and graphene, has been highly preferred due to their enhanced electromechanical properties. These conductive nanomaterials have shown excellent quantitative performance in terms of sensitivity and selectivity for the chosen aflatoxin compounds. This paper elucidates some of the significant examples of the CNTs and graphene-based sensors measuring Aflatoxin M1 (ATM1) and Aflatoxin B1 (AFB1) compounds at low concentrations. The fabrication technique and performance of each of the sensors are shown here, as well as some of the challenges existing with the current sensors.

Preparation of novel catalyst-free Fe3C nanocrystals encapsulated NCNT structured catalyst for continuous catalytic wet peroxide oxidation of phenol

Novel nitrogen-doped carbon nanotubes encapsulating Fe₃C nanocrystals coated paper-like sintered stainless steel fibers (PSSF) structured catalyst (Fe₃C@NCNT/PSSF) was designed for continuous catalytic wet peroxide oxidation of phenol. Firstly, Fe₃C@NCNT/PSSF was fabricated by directly growing the Fe₃C encapsulated NCNTs onto the three-dimensional PSSF substrate through CVD method using melamine as precursor, the monolithic PSSF substrate served as a self-catalyzing agent for catalyst preparation. Secondly, the surface morphology and structure of Fe₃C@NCNT/PSSF were investigated to optimize the synthesis condition. Then Fe₃C@NCNT/PSSF was employed as a structured catalyst for continuous CWPO of phenol, effect of operating conditions was studied. Catalytic results showed that the encapsulated Fe₃C nanoparticles significantly enhanced the degradation efficiency of phenol, and catalytic performance was improved with the increase of temperature. However, catalytic performance appeared unusual when residence time was considered, due to the effect of strongly polar surface of NCNTs on the contact efficiency between pollutants and hydroxyl radicals. Reusability experiments showed that catalytic performance of catalyst was improved with the increase of reusability cycles although the iron leaching concentration decreased, attributing to enhanced reaction within internal channel of Fe₃C@NCNT. The fourth reaction run achieved a stable phenol conversion of 90%, TOC conversion around 41% under optimized conditions.

Non-purified commercial multiwalled carbon nanotubes supported on electrospun polyacrylonitrile@polypyrrole nanofibers as photocatalysts for water decontamination

We present a photoactive composite material for water decontamination consisting of non-purified commercial multiwalled carbon nanotubes (CNT(NP)s) supported on an electrospun polymeric mat made of core-sheath polyacrylonitrile-polypyrrole nanofibers. This is the first system that specifically exploits the superior photocatalytic activity of CNT(NP)s compared with the purified carbon nanotubes usually employed. A CNT(NP) still contains the catalytic metal oxide nanoparticles (NPs) used for its synthesis, embedded in the nanotube structure. Under UV-visible irradiation, these NPs generate highly reactive ˙OH radicals capable of degrading the organic molecules adsorbed on the nanotube. Photocatalytic tests on the composite material show that CNT(NP)s act mostly as a source of photogenerated charge carriers. The adsorption of target substrates occurs preferentially onto the polypyrrole sheath, which shuttles the reactive carriers from CNT(NP)s to the substrates. In addition, UV-visible irradiation of semiconducting polypyrrole generates radical species that directly react with the adsorbed substrates. All synthetic procedures reported are scalable and sustainable. This mechanically resistant and flexible composite overcomes one of the weakest aspects of water treatments that employ suspended nanocatalysts, namely the expensive and poorly scalable recovery of the catalyst through nanofiltration. All these features are required for large-scale photocatalytic treatments of polluted water.

Purification for Carbon Nanotubes Synthesized by Flame Fragments Deposition via Hydrogen Peroxide and Acetone

Carbon nanotubes (CNTs) are synthesized by the flame fragment deposition (FFD) technique using Iraqi liquefied petroleum gas (LPG) as a source of carbon in a hand-made reactor at a low temperature (160 °C) without using a catalyst. Purification of the multi-walled carbon nanotubes (MWCNTs) is carried out using a two-step process consisting of sonication in 30 wt.% hydrogen peroxide (H₂O₂) solution at room temperature to remove amorphous impurities adhering to the walls of the CNTs and carbon nanoparticles (CNPs), followed by sonication in an acetone bath to remove the polyaromatic hydrocarbons (PAH) formed during the LPG gas burning. Comprehensive characterizations such as X-ray diffraction (XRD), atomic force microscopy (AFM), thermo-gravimetric analysis (TGA), and transmission electron microscopy (TEM) were conducted to verify the efficiency of the purification process. The results clearly demonstrated that this process is promising for the purification of the synthesized CNTs.

Room-temperature chemical synthesis of C2

Diatomic carbon (C2) is historically an elusive chemical species. It has long been believed that the generation of C2 requires extremely high physical energy, such as an electric carbon arc or multiple photon excitation, and so it has been the general consensus that the inherent nature of C2 in the ground state is experimentally inaccessible. Here, we present the chemical synthesis of C2 from a hypervalent alkynyl-λ3-iodane in a flask at room temperature or below, providing experimental evidence to support theoretical predictions that C2 has a singlet biradical character with a quadruple bond, thus settling a long-standing controversy between experimental and theoretical chemists, and that C2 serves as a molecular element in the bottom-up chemical synthesis of nanocarbons such as graphite, carbon nanotubes, and C60.

Highly Efficient and Stable Novel NanoBiohybrid Catalyst to Avert 3,4-Dihydroxybenzoic Acid Pollutant in Water

The present study reported for the first time covalent immobilization of protocatechuate 3,4-dioxygenase (3,4-POD) onto functionalized multi-walled carbon nanotubes (F-MWCNT) for degrading the toxic 3,4-dihydroxybenzoic acid (3,4-DHBA) pollutant in water. The F-MWCNTs had a maximum 3,4-POD loading of 1060 μg/mg. Immobilized 3,4 POD had 44% of relative structural changes to its free configurations. Nevertheless, >90% of relative activity and about 50% of catalytic efficiency were retained to the free enzyme. Immobilized 3,4-POD demonstrated higher alkaline stability and thermostability than the free 3,4-POD. The free and immobilized 3,4-POD lost 82% and 66% of relative activities, respectively after 180 min of incubations at 90 °C. Excellent shelf-life was observed for the immobilized 3,4-POD with residual activity of 56% compared with 41% and 39% of the free 3,4-POD at 4 °C and 25 °C over 30 days storage. Immobilized 3,4-POD showed >60% of catalytic activity retention even after ten-cycle uses, defraying the expenses of free 3,4-POD productions for long term uses. Finally, the immobilized 3,4-POD removed 71% of 3,4-DHBA from water in <4 h, paving its future application for water purification with reduced costs and time.

Nitrile N-oxides in programmable one-pot functionalization of multi-wall carbon nanotubes via 1,3-dipolar cycloaddition

Multi-wall carbon nanotubes (MWCNTs) were one-pot functionalized with a series of nitrile N-oxides as 1,3-dipoles carrying diverse functional groups.

Role of interfacial interactions to control the extent of wrapping of polymer chains on multi-walled carbon nanotubes

Transmission electron microscopic image of separated MWCNTs (N51L15G5) showing the wrapped polymer chains on the MWCNTs surface, which corresponds to the α-phase of the PP.

Carbon Nanotube Synthesis Using Coal Pyrolysis

This study investigates carbon nanotube (CNT) production from coal pyrolysis wherein the output gases are used in a chemical vapor deposition reactor. The carbon products are similar to those using commercial coal gas as feedstock, but coal is a relatively cheaper feedstock compared to high purity source gases. A Gibbs minimization model has been developed to predict the volume percentages of product gases from coal pyrolysis. Methane and carbon monoxide were the largest carbon components of the product stream and thus formed the primary source for CNT synthesis. Both the model and the observations showed that increasing the furnace temperature led to a decrease in the absolute quantities of "useful" product gases, with the optimal temperature between 400 and 500 °C. Based on the experimental data, a kinetic rate law for CNT from coal pyrolysis was derived as d[CNT]/dt = K([CO][CH4])(1/2), where K is a function of several equilibrium constants representing various reactions in the CNT formation process.

Double-walled carbon nanotube processing

Single-walled carbon nanotubes (SWCNTs) have been the focus of intense research, and the body of literature continues to grow exponentially, despite more than two decades having passed since the first reports. As well as extensive studies of the fundamental properties, this has seen SWCNTs used in a plethora of applications as far ranging as microelectronics, energy storage, solar cells, and sensors, to cancer treatment, drug delivery, and neuronal interfaces. On the other hand, the properties and applications of double-walled carbon nanotubes (DWCNTs) have remained relatively under-explored. This is despite DWCNTs not only sharing many of the same unique characteristics of their single-walled counterparts, but also possessing an additional suite of potentially advantageous properties arising due to the presence of the second wall and the often complex inter-wall interactions that arise. For example, it is envisaged that the outer wall can be selectively functionalized whilst still leaving the inner wall in its pristine state and available for signal transduction. A similar situation arises in DWCNT field effect transistors (FETs), where the outer wall can provide a convenient degree of chemical shielding of the inner wall from the external environment, allowing the excellent transconductance properties of the pristine nanotubes to be more fully exploited. Additionally, DWCNTs should also offer unique opportunities to further the fundamental understanding of the inter-wall interactions within and between carbon nanotubes. However, the realization of these goals has so far been limited by the same challenge experienced by the SWCNT field until recent years, namely, the inherent heterogeneity of raw, as-produced DWCNT material. As such, there is now an emerging field of research regarding DWCNT processing that focuses on the preparation of material of defined length, diameter and electronic type, and which is rapidly building upon the experience gained by the broader SWCNT community. This review describes the background of the field, summarizing some relevant theory and the available synthesis and purification routes; then provides a thorough synopsis of the current state-of-the-art in DWCNT sorting methodologies, outlines contemporary challenges in the field, and discusses the outlook for various potential applications of the resulting material.

Preparation, purification and characterization of high purity multi-wall carbon nanotube

Chemical vapor deposition (CVD) was optimized in order to prepare multi-wall carbon nanotubes (MWCNTs). Preparation of MWCNTs was achieved by the help of ferrocene as a catalyst with continuous flow of xylene. Morphology and structure of as grown and purified MWCNTs were characterized by Scanning Electron Microscope (SEM) and High-Resolution Transmission Electron Microscope (HRTEM). Energy Dispersive X-ray (EDX) spectra for the as grown MWCNTs confirm that the deposits are carbonaceous materials. XRD pattern of purified sample indicates that the Fe peaks at 44.6 and 50.9 have been decreased. This confirms that purification process is effectively reducing Fe component. Further qualitative information on the purification process are indicated and confirmed by the thermal analysis measurements. Finally, FTIR studies have been performed for the identification of the functional group attached on the surface of the MWCNTs. Collecting these results revealed that the optimized CVD is suitable for the production of MWCNTs.

A layer-nanostructured assembly of PbS quantum dot/multiwalled carbon nanotube for a high-performance photoswitch

A layered nanostructure of a lead sulfide (PbS) quantum dot (QD)/multi-walled carbon nanotube (MWNT) hybrid was prepared by the electrostatic assembly after the phase transfer of PbS QDs from an organic to an aqueous phase. Well-crystallized PbS QDs with a narrow diameter (5.5 nm) was mono-dispersed on the sidewalls of MWNT by the electrostatic adsorption. Near-infrared absorption of PbS/MWNT nanostructures was improved and controlled by the packing density of PbS QDs. Efficient charge transfer between PbS and MWNT at the interface resulted in a remarkable quenching of photoluminescence up to 28.6% and a blue-shift of emission band by 300 nm. This feature was facilitated by band energy levels based on the intimate contact through the electrostatic interaction. Two-terminal devices using PbS/MWNT nanostructures showed an excellent on/off switching photocurrent and good stability during 20 cycles under light illumination due to electron transfer from PbS to MWNT. The photoswitch exhibited a high photo sensitivity up to 31.3% with the photocurrent of 18.3 μA under the light of 3.85 mW/cm(2), which outperformed many QD/carbon-based nanocomposites. Results indicate that the electrostatic layered assembly of QD/MWNT nanostructure is an excellent platform for the fabrication of high-performance optoelectronic devices.

Improved polymer encapsulation on multiwalled carbon nanotubes by selective plasma induced controlled polymer grafting

Surface graft polymerization on multiwalled carbon nanotubes (MWCNTs) with several grafting mechanisms is nowadays a demanding field of nanocomposites in order to enhance the load carrying capacity, thus improving the overall performance of the composites. Here, we demonstrate the covalent grafting of a sulfonic acid terminated monomer, 2-acrylamido-2-methylpropane sulfonic acid onto sidewalls of MWCNTs via a comparative study between oxygen plasma induced grafting (OPIG), nitrogen plasma induced grafting (NPIG), and nitrogen + oxygen plasma induced grafting (NOPIG) with the aim to identify the most effective process for the preparation of polymer encapsulated carbon nanotubes. From the detail surface analysis, it has been noticed that NOPIG offered much better surface grafting than that of the OPIG and NPIG. The transmission electron microscopy (TEM) images showed that MWCNTs modified by NOPIG possess much thicker and uniform polymer coatings throughout. From thermogravimetric analysis (TGA), the grafting degree was found to be ~80 wt % for the NOPIG sample.

Infrared-actuated recovery of polyurethane filled by reduced graphene oxide/carbon nanotube hybrids with high energy density

Optically actuated shape recovery materials receive much interest because of their great ability to control the creation of mechanical motion remotely and precisely. An infrared (IR) triggered actuator based on shape recovery was fabricated using polyurethane (TPU) incorporated by sulfonated reduced graphene oxide (SRGO)/sulfonated carbon nanotube (SCNT) hybrid nanofillers. Interconnected SRGO/SCNT hybrid nanofillers at a low weight loading of 1% dispersed in TPU showed good IR absorption and improved the crystallization of soft segments for a large shape deformation. The output force, energy density and recovery time of IR-triggered actuators were dependent on weight ratios of SRGO to SCNT (SRGO:SCNT). TPU nanocomposites filled by a hybrid nanofiller with SRGO:SCNT of 3:1 showed the maximum IR-actuated stress recovery of lifting a 107.6 g weight up 4.7 cm in 18 s. The stress recovery delivered a high energy density of 0.63 J/g and shape recovery force up to 1.2 MPa due to high thermal conductivity (1.473 W/mK) and Young's modulus of 23.4 MPa. Results indicate that a trade-off between the stiffness and efficient heat transfer controlled by synergistic effect between SRGO and SCNT is critical for high mechanical power output of IR-triggered actuators. IR-actuated shape recovery of SRGO/SCNT/TPU nanocomposites combining high energy density and output forces can be further developed for advanced optomechanical systems.

Enhanced Photocatalytic Degradation of Methylene Blue Using ZnFe2O4/MWCNT Composite Synthesized by Hydrothermal Method

Multiwalled carbon nanotubes (MWCNTs) were synthesized using arc discharge method at a magnetic field of 430 G and purified using HNO3/H2O2. Transmission electron micrographs revealed that MWCNTs had inner and outer diameter of ~2 nm and ~4 nm, respectively. Raman spectroscopy confirmed formation of MWCNTs showing G-band at 1577 cm−1. ZnFe2O4 and ZnFe2O4/MWCNT were produced using one step hydrothermal method. Powder X-ray diffraction (XRD) confirmed the formation of cubic spinel ZnFe2O4 as well as incorporation of MWCNT into ZnFe2O4. Visible light photocatalytic degradation of methylene blue (MB) was studied using pure ZnFe2O4 and ZnFe2O4/MWCNT. The results showed that ZnFe2O4/MWCNT composite had higher photocatalytic activity as compared to pure ZnFe2O4. After irradiation for 5 hours in the visible light, MB was almost 84% degraded in the presence of ZnFe2O4 photocatalyst, while 99% degradation was observed in case of ZnFe2O4/MWCNT composite. This enhancement in the photocatalytic activity of composite may be attributed to the inhibition of recombination of photogenerated charge carriers.

Effect of Magnetic Field on the Growth of Aligned Carbon Nanotubes Using a Metal Free Arc Discharge Method and their Purification

Multiwalled Carbon Nanotubes (MWCNTs) have been synthesized using a low cost arc discharge method without using metal catalyst and vacuum devices. Effect of magnetic field on the synthesis of MWCNTs and their purity has been scrutinized. A magnetic field of 310 gauss has been found to give better purity of carbon nanotubes as confirmed by Raman spectroscopy. However, the removal of amorphous carbon from the surface of so prepared multiwalled carbon nanotubes has been achieved by different oxidizing conditions. It has been observed that the maximum removal of amorphous carbon found by using the strong oxidizing agent HNO3/H2O2. This strong oxidizing agent HNO3/H2O2 removes most of the carbonaceous impurities leading to thermal stability of carbon nanotubes suggested by thermo gravimetric analysis. X-ray diffraction show the formation of carbon nanotubes having a peak indexed at (002) as the fingerprint for multiwalled carbon nanotubes. Fourier Transform Infrared (FTIR) spectra confirmed the formation of the multiwalled carbon nanotubes showing a characteristic stretching band at 1615 cm-1 corresponding to the C=C bonds of tubular carbon. Raman spectroscopy revealed invaluable insights into the purification of nanotubes. G-band (1577 cm-1) corresponds to the confirmation of MWCNTs. Defect induced D-band (1355 cm-1) has been minimized after purifying CNTs with HNO3/H2O2 for 24 hrs. Transmission Electron microscopic (TEM) studies indicate the formation of CNTs with controlled alignment having diameter in the range 2-8 nm.

The road for nanomaterials industry: a review of carbon nanotube production, post-treatment, and bulk applications for composites and energy storage

The innovation on the low dimensional nanomaterials brings the rapid growth of nano community. Developing the controllable production and commercial applications of nanomaterials for sustainable society is highly concerned. Herein, carbon nanotubes (CNTs) with sp(2) carbon bonding, excellent mechanical, electrical, thermal, as well as transport properties are selected as model nanomaterials to demonstrate the road of nanomaterials towards industry. The engineering principles of the mass production and recent progress in the area of CNT purification and dispersion are described, as well as its bulk application for nanocomposites and energy storage. The environmental, health, and safety considerations of CNTs, and recent progress in CNT commercialization are also included. With the effort from the CNT industry during the past 10 years, the price of multi-walled CNTs have decreased from 45 000 to 100 $ kg(-1) and the productivity increased to several hundred tons per year for commercial applications in Li ion battery and nanocomposites. When the prices of CNTs decrease to 10 $ kg(-1) , their applications as composites and conductive fillers at a million ton scale can be anticipated, replacing conventional carbon black fillers. Compared with traditional bulk chemicals, the controllable synthesis and applications of CNTs on a million ton scale are still far from being achieved due to the challenges in production, purification, dispersion, and commercial application. The basic knowledge of growth mechanisms, efficient and controllable routes for CNT production, the environmental and safety issues, and the commercialization models are still inadequate. The gap between the basic scientific research and industrial development should be bridged by multidisciplinary research for the rapid growth of CNT nano-industry.

Highly conductive carbon nanotube matrix accelerates developmental chloride extrusion in central nervous system neurons by increased expression of chloride transporter KCC2

Exceptional mechanical and electrical properties of carbon nanotubes (CNT) have attracted neuroscientists and neural tissue engineers aiming to develop novel devices that interface with nervous tissues. In the central nervous system (CNS), the perinatal chloride shift represents a dynamic change that forms the basis for physiological actions of γ-aminobutyric acid (GABA) as an inhibitory neurotransmitter, a process of fundamental relevance for normal functioning of the CNS. Low intra-neuronal chloride concentrations are maintained by a chloride-extruding transporter, potassium chloride cotransporter 2 (KCC2). KCC2's increasing developmental expression underlies the chloride shift. In neural injury, repressed KCC2 expression plays a co-contributory role by corrupting inhibitory neurotransmission. Mechanisms of Kcc2 up-regulation are thus pertinent because of their medical relevance, yet they remain elusive. Here, it is shown that primary CNS neurons originating from the cerebral cortex, cultured on highly-conductive few-walled-CNT (fwCNT) have a strikingly accelerated chloride shift caused by increased KCC2 expression. KCC2 upregulation is dependent on neuronal voltage-gated calcium channels (VGCC) and, furthermore, on calcium/calmodulin-dependent kinase II, which is linked to VGCC-mediated calcium-influx. It is also demonstrated that accelerated Kcc2 transcription in brain-slices prepared from genetically-engineered reporter mice, in which Kcc2 promoter drives luciferase, when the cerebral cortex of these mice is exposed to fwCNT-coated devices. Based on these findings, whether fwCNT can enhance neural engineering devices for the benefit of neural injury conditions associated with elevated neuronal intracellular chloride concentration-such as pain, epilepsy, traumatic neural injury and ischemia-can now be addressed. Taken together, our novel insights illustrate how fwCNTs can promote low neuronal chloride in individual neurons and thus inhibitory transmission in neural circuits.